1. Field of the Invention
This invention relates to a leakage-free feed roll assembly for an extruder machine. Specifically, this invention relates to a feed roll assembly for reducing the leakage of elastomeric material in a feed section of an extruder machine.
2. Description of Related Art
Extruder screws employed in the softening or melting, mixing, and compounding of elastomeric material typically employ three zones, namely a feed zone, a softening or melting zone, and a metering zone. The extruder screw is typically positioned for rotation in an extruder barrel that includes a hopper or other guarding section adjacent to the feed section of the screw, and a discharge end opposite the hopper or guarding section and proximate to the metering section of the screw. A solid elastomeric material is introduced through the hopper or guarding section during operation and presented to the feed zone of the screw where it begins to soften or melt. The solid elastomeric material is then conveyed to the softening or melting zone where it softens or melts at a greater rate than in the feed zone and is ultimately converted to a molten state. The molten material is transferred from the softening or melting zone to the metering zone for conveyance to a discharge end of the extruder where the material typically passes through a shaping die.
FIG. 1 illustrates a conventional feed roll assembly in a feed section of an extruder machine. The feed section 100 of the extruder machine is encased in a housing 102 that includes a barrel (not shown) having a bore 104. The feed section 100 is generally mounted to a gear reducer and includes a hopper or guarding section adjacent thereto. An axially elongated extruder screw 106 is positioned within the bore 104 and is rotatably coupled to the gear reducer. The extruder screw 106 is divided into three zones or sections, a feed section 100 located at an inlet end of the extruder screw 106, a metering section located at an outlet end of the extruder screw, and a transition section positioned between the feed section 100 and the metering section.
Solid elastomeric material is introduced into a feed opening 108 of the barrel through the hopper or guarding section during operation of the extruder machine. The solid elastomeric material is carried by a feed roll 112 into the extruder screw 106 where it is advanced into the transition section. The solid elastomeric material is converted into a molten state as it is advanced along the transition section and is then fed into the metering section. The metering section then conveys the molten material out of the extruder usually through a shaping die mounted on the outlet end of the barrel.
Extruder machines typically employ a conventional rotating, driven, auxiliary feed roll 112 to facilitate the feed of the elastomeric material from the feed opening 108 into the extruder screw 106 in the feed section 100. The elastomeric material is very stiff and viscous when introduced through the feed opening 108 of the feed section 100 and tends to roll on top of the extruder screw 106 and does not become engaged between flights of the extruder screw 106 without the aid of the conventional feed roll 112. The conventional feed roll 112 rotates in a direction counter to the rotation of the extruder screw 106 and creates a roll nip that pinches and impinges the elastomeric material into the extruder screw 106. The extruder screw 106 then conveys the elastomeric material to the transition zone (not shown).
FIG. 2 illustrates a conventional feed roll assembly. The conventional feed roll assembly 200 includes a drive shaft end 202 of a feed roll 204 that is connected to a gear reducer and rotates the feed roll 204 during operation. The feed roll 204 includes a free end 206. The drive shaft end 202 and the free end 206 of the feed roll 204 are coupled to support arms 208 of a feed roll support 210. The use of the conventional feed roll assembly 200 is problematic because of the danger of the elastomeric material being forced into leakage paths L surrounding the feed roll 204 due to pressures generated in the feed section. Such leakage paths L include a clearance between support arms 208 and the feed roll 204, a clearance above and a clearance below the feed roll support 210 and the feed roll 204, and a clearance between the feed roll support 210 and the feed roll 204 (also see L in FIG. 1). If the feed roll 204 is not thoroughly and regularly cleaned during interruption in the operation of the extruder, then the elastomeric material located in the leakage paths L hardens and blocks the feed roll 204 when operation of the extruder is resumed. The leaked elastomeric material becomes scrap or waste and is a lost revenue that creates additional clean-up and maintenance of the extruder machine. The leaked elastomeric material also generates extensive wear on the extruder machine and causes the machine to wear more rapidly.
Attempts to reduce the leakage paths surrounding conventional feed rolls are known in the art. One such attempt proffers the use of two separable, rotating seal rings and a feed roll housing. Each rotating seal ring is fastened to an end of the feed roll and rotates with the feed roll. Each seal ring encompasses the entire end portions of the feed roll. The seal rings contain grooves for returning leaked elastomeric material to the active face of the feed roll during operation of the extruder machine. This design also encloses approximately fifty percent of the feed roll with a feed roll housing. The feed roll housing has a single, constant bore diameter. This design, however, fails to provide an efficient leakage-free feed roll assembly. While this design does enclose the feed roll, it fails to redirect the elastomeric material towards the center of the active face of the feed roll and away from the feed roll end seals.
There is a need in the industry for a feed roll assembly design that provides desirable feedback of overflow elastomeric material and permits a retrofitting of the feed roll assembly to existing extruder machines.